1. Field of the Invention
The present invention relates to a display device incorporating an organic electroluminescence (EL) device and, more particularly, to a display device incorporating an organic EL device capable of enhancing light utilization efficiency from the top of the display device.
2. Description of the Related Art
A technical problem for organic EL devices, such as organic light-emitting diodes (OLEDs) is low light extraction efficiency. Light extraction efficiency may be generally defined as the fraction of light radiated outside of the OLED out of the out of the total optical power generated in the active layer (light-emitting layer) of the OLED. In these terms, the extraction efficiency of an organic EL device is low because, since light is emitted at various angles from a light emitting layer in the organic EL device, total reflection components often appear at the interface between a protective layer and an external space and thereby the emitted light is trapped inside the organic EL device. Various configurations have been proposed to overcome this problem. Japanese Patent Laid-Open No. 2004-39500 discloses a configuration for enhancing the light extraction efficiency from the top of an organic EL device by disposing a resin-made lens array on an oxidized silicon nitride (SiNxOy) film which seals the organic EL device.
In the configuration in which a lens array is situated on an organic EL device disclosed in Japanese Patent Laid-Open No. 2004-39500, a light condensing effect may be produced in addition to an extraction effect of the total reflection components. These effects can enhance brightness (i.e., light emission efficiency) of the display device incorporating an organic EL device by condensing light at the top (center) of each lens in the lens array. In the form disclosed in Japanese Patent Laid-Open No. 2004-39500, however, brightness of the display device in oblique directions (peripheral region of the lens) is low and therefore radiation angle characteristics are negatively affected.